The inspection of labeled containers for intactness is usually done by imaging. For this, it is known, for example, from WO 03/104780 A1, to let a product stream composed of filled and labeled containers pass by an illuminated screen and to record the labels with a camera. Labels, being absorbent in the ultraviolet or infrared spectral range, produce a contrast against the filled bottle for detecting holes in the label.
JP 2008-281477 A further describes a method for inspecting transparent labels on transparent plastic bottles. By irradiation with ultraviolet light, fluorescence is excited in the labels, which can be represented as a difference in contrast to the non-fluorescent container. Holes and tears can thereby also here be detected as brightness differences in the fluorescence representation.
Unlike holes, bubbles and/or creases on labels cause relatively low contrasts in a representation by imaging, which is usually also overlaid with the necessarily high-contrast label prints. Bubbles and/or creases can therefore not be detected with sufficient reliability using a single camera image. Commercially available inspection apparatuses for bubbles and/or creases therefore draw on stored reference images of the label to be inspected.
However, numerous problems arise when operating such systems. For example, the label print quality among different label batches can vary, so that the reference recordings not only need to be updated regularly but also must be correctly assigned during operation. Since updating and teaching of the inspection apparatuses can not be fully automated, operator errors could possibly cause significant risks in quality control. In addition, the accuracy of the print and the labeling is critical for a comparison with previously stored images and therefore for reliable detection of bubbles and/or creases.
Furthermore, differently labeled products, such as with labels in different languages, involves an enormous effort due to frequent updating and teaching of such inspection systems. Overall, the administration of the reference images and the teaching involves a very high effort for maintenance and operation of the inspection systems and for the training of operating personnel. There is therefore a need to improve the known methods and apparatuses in this regard.